add Qt property declarations

lib/customshadoweffect.h

@@ -9,6 +9,11 @@
 class CustomShadowEffect : public QGraphicsEffect
 {
     Q_OBJECT
+
+    Q_PROPERTY(qreal distance WRITE setDistance READ distance)
+    Q_PROPERTY(qreal blurRadius WRITE setBlurRadius READ blurRadius)
+    Q_PROPERTY(qreal color WRITE setColor READ color)
+
 public:
     explicit CustomShadowEffect(QObject *parent = 0);